1. Field of the Invention
This invention pertains to a method for treating wells penetrating and completed in subterranean earth formations, and more particularly to a method for treating a petroleum containing formation in the immediate vicinity of a well so as to stabilize unconsolidated sands to prevent their migration into or away from the well. More particularly, this invention pertains to a method of treating such wells with granular material saturated with bitumen and then contacted with steam and air in a controlled ratio to effect low temperature controlled oxidation of bituminous petroleum so as to form a cokelike material which bonds sand or gravel grains together to form a permeable zone around the well to restrain movement of the sand.
2. Prior Art and Background
Recovery of fluids such as gas and/or petroleum from a subterranean formation is frequently found to be troublesome when the subterranean formation is composed of one or more incompetent sand layers or zones. The sand particles in the incompetent or unconsolidated sand zone move or migrate into the well bore during recovery of formation fluids from that particular zone, or sand particles move away from the well during the injection of secondary or tertiary recovery fluids into the formations. In the instance of recovering fluid from the formation, the movement of sand into the well bore can cause the well to cease production of fluids therefrom. Also, small sand particles can plug small openings in porous masses formed around the well bore for the purpose of restraining flow of particulate matter such as sand or gravel into the well, resulting in terminating further production of fluid from that particular well. Another adverse result of sand particle migration from the producing well bore is associated with the fact that fine sand may be transported to the surface of the earth and carried along through pipes, pumps and other surface equipment being used to recover formation fluids. Such sand particles are abrasive, and rapid wear results to the pumps and other mechanical equipment contacted thereby.
Many methods are described in the prior art for preventing or decreasing flow of undesirable sand particles during the course of recovering formation fluids from production wells, such as by the placement of sand screens, filters, perforated or slotted liners, etc. around the well. These prior attempts have been successful in some instances, but have not always been entirely satisfactory for a number of reasons. Mechanical devices frequently restrain only the larger particle size sand, and are not completely effective at restraining or preventing the flow of fine particles from the formation into the well and ultimately into the surface located production equipment. Furthermore, such devices interfere with various types of completion and workover operations. More recently, chemical compositions which bond sand grains together with a resinous plastic material to form a permeable mass which effectively restrains the flow of sand particles from the formation have been proposed in the prior art and used in field operations. These methods usually involve injecting into the subterranean formation a polymerizable resinous material, which can be caused to polymerize later so as to consolidate formation sand to form the desired permeable barrier in the formation. Numerous difficulties have been encountered in commercial application of this technique including the difficulty of achieving even polymerization of the resinous material in the formation to a degree necessary to consolidate these formations, while still maintaining adequate permeability so as to permit flow of formation fluids therethrough. Furthermore, these resinous materials are quite expensive in comparison to the more traditional mechanical methods.
In the instance of recovering viscous petroleum from subterranean formations such as tar sand or bituminous sand deposits some form of treatment which renders the highly viscous petroleum sufficiently mobile that it will flow to the production well and then to the surface of the earth must be used. The most commonly utilized heating fluid for achieving the required viscosity reduction in bituminous petroleum is high temperature steam which is injected into the well with production of steam and emulsified bitumen from remotely located production wells. High temperature steam which frequently also contains appreciable quantities of an alkaline substance such as sodium-hydroxide, cannot be used with resinous sand consolidating materials because these materials are rapidly dissolved or degraded by contact with hot alkaline steam.
In view of the foregoing discussion it can be appreciated that there is a substantial, unfulfilled need for a sand control method capable of preventing flow of unconsolidated sand particles into a well bore or away from a well bore during a period of injection fluids thereinto. More particularly there is a need for an inexpensive, reliable method of controlling sand in a formation having an appreciable quantity of unconsolidated sand particles, which method will result in a permeable mass which will not be affected by subsequent contact with high temperature, alkaline fluids such as steam and caustic.
By the method of the present invention one is able to treat underground formation so as to effect consolidation of granular material such as sand and gravel into a permeable mass which will effectively restrain the movement of unconsolidated sand particles into or out of the well bore, which consolidated permeable mass will not be appreciably effected by subsequent contact with hot alkaline fluids such as steam and caustic and thus avoid many of the disadvantages of the prior art methods, both mechanical and chemical.